LED lamps greatly reduce operating cost compared to incandescent lamps, are more pleasing than fluorescent lamps, and have a very long life.
The present assignee has previously invented a flat light sheet formed by printing microscopic vertical LED dies over a conductor layer on a flexible substrate to electrically contact the LED's bottom electrodes, then printing a thin dielectric layer over the conductive layer which exposes the LED's top electrodes, then printing another conductor layer to contact the LED's top electrodes. The LED dies are printed to have the same orientation, such as anode electrodes up. The LEDs are thus connected in parallel. By applying a correct polarity voltage across the conductor layers, the LEDs are illuminated. By using a transparent film as the substrate and making either or both of the conductor layers transparent, light may exit through either surface or both surfaces simultaneously. If the LEDs are GaN-based and emit blue light, a phosphor layer (e.g., YAG) may be deposited over the light emitting surface to cause the light sheet to emit any color light, such as white light. The light sheets may be formed to have a thickness less than 2 mm.
Further detail of forming a light source by printing microscopic vertical LEDs, and controlling their orientation on a substrate, can be found in US application publication US 2012/0164796, entitled, Method of Manufacturing a Printable Composition of Liquid or Gel Suspension of Diodes, assigned to the present assignee and incorporated herein by reference.
Paragraph 0435 of the publication US 2012/0164796 describes how the flexible light sheet “may be curled, folded, twisted, spiraled, flattened, knotted, creased, and otherwise shaped into any of various forms and designs, of any kind, including architectural shapes, folded and creased origami shapes of other artistic or fanciful designs, Edison bulb shapes, fluorescent bulb shapes, chandelier shapes, for example and without limitation, . . . ”. As seen, the publication describes how the various shapes are achieved by some sort of bending of the light sheet and, since the light sheet is somewhat resilient, the resulting shape must be retained by some sort of external support structure, such as an Edison base.
The above-quoted disclosed uses of the flexible light sheet are still limited since fine 3-dimensional shapes could not be made using the disclosed techniques. For example, the light sheet could not be folded to produce an array of rounded bumps that change the emission profile and/or increase light extraction. Additionally, it would be desirable to provide a light sheet having 3-dimensional features where the features are not required to be retained by an external support structure. Additionally, it would be desirable to form the fine 3-dimensional features without the various layers of the light sheet delaminating from each other.